Just as a little background, this pertains to my 05 GT, so it came with the hardened 4th gear hub from the factory and shouldn't be related to the splines on the hub. It's currently got a little over 100K miles on it. A few months ago I went in through my side cover to finally take care of my pressure control solenoid (thanks go out to Bill for the very helpful side cover access guide). It was causing Max Adapt shifts before a Transgo shift kit and clunking into gear from a stop.
While in there I replaced the PCS, the TCC solenoid, and both shift solenoids, all AC Delco except the TCC which was a Borg Warner. I also popped in a Sonnax aftermarket boost valve and sleeve kit, and the 3-4 portion of the Transgo shift kit. New gaskets everywhere applicable, everything seemed to go well. The only hitch (which I think may be related to my issue) was that my 4th frictions and steels came out with the channel plate and proceeded to fall into my drain pan containing both tranny fluid and a little residual engine oil. I grabbed them and popped them back in place along with the thrust washer, but probably in a different orientation than they originally sat (I did make sure the frictions were between the steels like they should be). In terms of condition, they were visibly "scorched" if that's the word. I was a bit annoyed I did that, but tossed everything back together as-is since this is my DD. Transmission worked amazing since then.
Now fast forward to a week ago. I'm driving home from class on the highway doing around 70 mph. I move over a lane and give a little gas to get past a semi while in 4th gear, and the RPM's just fly up, no acceleration. 4th gear is just gone. Nothing but slip no matter the speed or acceleration, but the RPM's are still lower than 3rd gear, so I can tell it's technically "engaged". Pop it into 3rd, no problems at all, TCC still locks and unlocks as needed and 1st through 3rd upshift and downshift with no issue. I've just been driving with the shifter in "3" to avoid it.
So... with all that out of the way, would I be correct in thinking my 4th frictions are done? Like I mentioned, it's an 05 so I would think the hub splines should be fine, and if it was solenoid related I'd be having other issues as well. My thoughts are to go back in the cover next month between semesters and replace the 4th clutch set entirely, maybe even put a new o-ring on the 4th accumulator since I could have possibly messed that up while installing the 3-4 portion of the shift kit. New fluid and filter too since it couldn't hurt. Some opinions would be appreciated though, I could be missing something when it comes to 4th gear operation in these transmissions.
